The invention provides a low-pressure casting process of a water way plate. The low-pressure casting process includes the steps that a low-pressure casting die is provided, the die is provided with acavity corresponding to the structure of the water way plate, a sand core is arranged in the cavity, and the structure of the sand core corresponds to the structure of a water way cavity of a water way; a pressure casting material is added into the cavity of the low-pressure casting die, and pressure casting is carried out under the conditions of low pressure and high pressure; and after pressurecasting forming is completed, the sand core in the cavity is baked into fine ash under the high-temperature condition, and the formed water way plate is separated from the sane core baked into the fine ash. According to the low-pressure casting process of the water way plate, an integrated pressure casting forming manner is adopted, the water way plate with a slope structure can be manufactured, compared with an existing friction welding process, the water leakage risk caused by the friction process is greatly reduced, while integrated forming casting of the water way plate is facilitated, thequality of the water way plate is improved, and the safety of the product is improved.